EDINBURGH/LONDON (Reuters) - A poll
showing support for Scottish independence at its highest ever level
threw the fate of the United Kingdom into question on Tuesday, just two
weeks before Scots vote on whether to secede.

The poll by YouGov showed the unionist lead had shrunk to 6
percentage points from 22 a month ago as support for independence
jumped to 47 percent in August, suggesting a major shift in opinion
ahead of the September 18 referendum.

After months of polls showing nationalists heading for defeat in the
vote, the YouGov poll for the first time raises the real prospect
that secessionists could achieve their goal of breaking the
307-year-old union with England.

"A ‘Yes’ victory is now a real possibility," YouGov President Peter
Kellner, one of Britain's most respected pollsters, said. "A close
finish looks likely."

Polls show different levels of support for the unionist campaign and
although none have shown the independence camp in the lead, the
sudden surge indicated by the poll electrified Britain's political
class after its summer break.

A vote to breakaway would be followed by negotiations with London on
what to do about sterling, the national debt, North Sea oil and the
future of Britain's nuclear submarine base in Scotland ahead of
independence pencilled in for March 24, 2016.

If Scots voted to leave the United Kingdom, Prime Minister David
Cameron would face calls to resign ahead of a national election in
May 2015 while Labour's chances of gaining a majority could be
scuppered if it lost its Scottish lawmakers.

Sterling fell to near a five-month low against the dollar and also
slipped versus a generally weak euro on Tuesday, while the cost of
hedging against sharp swings in the pound rose as investors sought
to insure against the risk of secession.

Traders saw further losses as the vote approaches.

"A Scottish 'Yes' to independence poses far more questions than it
answers but my best guess is that a 'Yes' would trigger a 3-5
percent fall by sterling as an initial reaction," said Kit Juckes,
currency analyst at Societe Generale.

CLOSE FINISH?

YouGov's Kellner, 67, said the poll data was so astounding that when
he first saw it, he double checked to see if there had been a
sampling error. But he said that after checking the data, he was
certain a real movement had taken place.

"When I first saw our data, I wanted to make sure the movement was
real," he said. "I am certain it is."

The poll was carried out on Aug. 28-Sept. 1 and 1,063 people were
questioned.

When respondents were asked how they would vote in the referendum,
42 percent said they would vote for independence while 48 percent
said they would vote against. Eight percent said they did not know
and 2 percent did not intend to vote.

It was the first time YouGov has showed support for "Yes" above 40
percent and support for "No" below 50 percent. About 4 million
Scottish residents have a vote in the referendum, so the poll
indicates 320,000 voters are still undecided.

By excluding those not intending to vote or undecided, the poll
showed support for keeping the union at 53 percent against 47
percent seeking independence.

"The 'Yes' campaign has both gained converts, and secured a
two-to-one lead among people who were undecided and have now taken
sides," Kellner said.

Supporters of the Labour party, traditionally the dominant political
force in Scotland, had become more supportive of independence, while
economic worries about the prospect of independence had diminished,
YouGov said.

Scottish nationalists said the poll, which comes just over a week
after pro-independence leader Alex Salmond won a television debate,
was a breakthrough moment in the campaign.

"More and more people are beginning to realise that a 'Yes' vote is
Scotland's one opportunity to make that enormous wealth work better
for everybody who lives and works here," said Blair Jenkins, head of
the independence campaign team.

Bookmaker Ladbrokes said that the odds on a vote in favour of
independence had narrowed overnight since the poll to 11/4, meaning
punters now put the likelihood of a split at its highest since May
this year. That continued a narrowing trend seen since the first
television debate in August when the odds were 5/1.

"Since the second debate we've been taking upwards of 5,000 pounds
worth of bets a day for 'Yes' from all over Scotland," said
Ladbrokes spokesman Alex Donohue. "It's basically one way traffic at
the moment."

(Additional reporting by William James and Anirban Nag in London;
Editing by Catherine Evans)